Filter cap at dc motor input
in [Design]
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From: pimpom on 21 Jul 2010 10:42 Grant wrote: > On Wed, 21 Jul 2010 10:38:54 +0530, "pimpom" > <pimpom(a)invalid.invalid> > wrote: > >> Grant wrote: >>>> >>> So tip your circuit upside down and pop in a P-channel >>> MOSFET? >>> >> I've thought of that as a possible solution, but for various >> reasons not a practical one in this case: 1) I don't have a >> P-channel MOSFET in stock (I can never remember to include it >> in >> my orders). 2) It's not locally available in my small town. > > I live in a biggish small town, can get overnight deliveries > from > Sydney, about 1000km away :) Judged by population, my town is not truly small with about 200,000 souls. But it's the capital of one of the less developed states of India in a remote corner of the country, with poor facilities and resources. (We have little in common with the rest of the nation). The problem of ordering from other parts of the country has less to do with our location than with the mentality of Indian business people. > >> Placing small orders from another city is not as easy in India >> as >> it is in places like the US. >> Unless it's absolutely necessary, >> I want to avoid having to start the pcb design, construction >> and >> assembly all over again. > > That's a really good reason. So you add inductor to isolate > the > cap, or rip cap out of motor? > For the time being, I've gone the route of reducing the caps from 1uF to 0.01uF. This was the easiest solution, esp. as I'd already opened the motor. It worked fine and the owners are enthusiastic about being able to use their machine again. I'm going back tomorrow for extended trials and final tweaking. I'll also try to find some way of estimating the amount of RFI (I don't have dedicated instruments for that). > I prefer leaving the motors alone, because a replacement down > the > track will cause same problem if 'they' forget to take out the > cap. > There's that, yes. I have not yet completely ruled out inserting a series inductor. OTOH, it's very unlikely that anyone else will work on the machine during its lifetime.
From: Grant on 21 Jul 2010 18:55
On Wed, 21 Jul 2010 20:12:42 +0530, "pimpom" <pimpom(a)invalid.invalid> wrote: >Grant wrote: >> On Wed, 21 Jul 2010 10:38:54 +0530, "pimpom" >> <pimpom(a)invalid.invalid> >> wrote: >> >>> Grant wrote: >>>>> >>>> So tip your circuit upside down and pop in a P-channel >>>> MOSFET? >>>> >>> I've thought of that as a possible solution, but for various >>> reasons not a practical one in this case: 1) I don't have a >>> P-channel MOSFET in stock (I can never remember to include it >>> in >>> my orders). 2) It's not locally available in my small town. >> >> I live in a biggish small town, can get overnight deliveries >> from >> Sydney, about 1000km away :) > >Judged by population, my town is not truly small with about >200,000 souls. But it's the capital of one of the less developed >states of India in a remote corner of the country, with poor >facilities and resources. (We have little in common with the rest >of the nation). The problem of ordering from other parts of the >country has less to do with our location than with the mentality >of Indian business people. Ah. My country town is large (for Victoria, it's fourth largest in state) at around 100k population, but we're only 160km from Melbourne, so overnight from Sydney to Melbourne, then a two hour drive up to Bendigo, delivery here around lunchtime :) It's good. > >> >>> Placing small orders from another city is not as easy in India >>> as >>> it is in places like the US. >>> Unless it's absolutely necessary, >>> I want to avoid having to start the pcb design, construction >>> and >>> assembly all over again. >> >> That's a really good reason. So you add inductor to isolate >> the >> cap, or rip cap out of motor? >> >For the time being, I've gone the route of reducing the caps from >1uF to 0.01uF. This was the easiest solution, esp. as I'd already >opened the motor. It worked fine and the owners are enthusiastic >about being able to use their machine again. I'm going back >tomorrow for extended trials and final tweaking. I'll also try to >find some way of estimating the amount of RFI (I don't have >dedicated instruments for that). A normal AM radio tuned off-station would tell you something, perhaps TV or shortwave Rx for higher frequencies? Compare with RF noise from other devices. > >> I prefer leaving the motors alone, because a replacement down >> the >> track will cause same problem if 'they' forget to take out the >> cap. >> >There's that, yes. I have not yet completely ruled out inserting >a series inductor. OTOH, it's very unlikely that anyone else will >work on the machine during its lifetime. Then you're in control :) Cheers, Grant. |